1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an electrode wiring structure of a liquid crystal display device.
2. Description of the Related Art
The official Gazette of JP-A-3-182723 describes a gate wiring of a liquid crystal display made of a lamination of a polysilicon film having a high impurity concentration and an aluminum (Al) film.
The official Gazette of JP-A-5-55575 describes a wiring of a liquid crystal display made of a metal material having a low resistance and anti-chemicals performance: alloy of tantalum (Ta) and niobium (Nb); Nb; or metal containing Nb as its main component.
The official Gazette of JP-A-2-106723 proposes a thin film transistor TFT having a gate wiring made of a lamination of Nb and Ta stacked in this order from the substrate side, the surface of the lamination being oxidized, and a gate insulating film made of silicon oxide (SiO2) or silicon nitride (SiN) stacked upon the gate electrode lamination. This Gazette describes that as compared to a Ta single layer, the resistance can be lowered and it is effective for preventing a short circuit between a gate line and a drain line.
The Gazette of JP-7-147852 proposes to use Nb for all or at least ones of gate and drain electrodes. This Gazette describes that an electrode structure having an improved throughput, a low resistance, and a low stress, and being easy to dry-etch can be realized because a two-layer structure made of such as alloy and different metal materials is not incorporated.
The Gazette of JP-A-2-232627 describes an auxiliary wiring formed on a scan line, the auxiliary wiring being made of Ti, Zr, Hf, V, Nb or the like, or nitride thereof and having a low resistance and a low contact resistance relative to the scan line.
A wiring of a conventional liquid crystal display device, particularly a gate electrode made of Al, is associated with the following problems. Hillocks or whiskers are formed during a heat treatment for an interlayer insulating film because of a low melting point (660.4xc2x0 C.) of Al, a rounded drive waveform is formed by a wiring resistance rise because of poor resistance to thermal oxidation of Al, or a short circuit between wirings is formed.
An Al film is patterned generally through wet etching to form a wiring pattern. Therefore, it is difficult to control the shape of a peripheral wall of the etched wiring, which may easily cause a defective portion around an interlayer insulating film and a drain electrode wiring, resulting in a short circuit between wirings and a breakage of a drain line.
It is an object of the present invention to provide a liquid crystal display device having a wiring structure excellent in resistance to thermal oxidation.
According to one aspect of the present invention, a metal wiring of a liquid crystal display device has a lamination structure of a first layer made of Nb or alloy containing Nb as a main component thereof and a second layer made of nitride of Nb or alloy containing Nb as a main component. With this lamination structure, resistance to thermal oxidation of the metal wiring can be improved. If the resistance of the metal wiring poses not practical problem, the metal wiring may be a single layer made of nitride of Nb or alloy containing Nb as a main component, by omitting the first layer made of Nb or alloy containing Nb as its main component. With this single layer structure, the resistance to thermal oxidation can also be improved.
If a third layer made of nitride of Nb or alloy containing Nb as a main component is formed under the first layer, it is possible to prevent a direct contact of the first layer with another layer different from the third layer. Nitride of Nb or alloy containing Nb as its main component properly matches another layer, particularly an insulating film. It is therefore possible to prevent a resistance increase and a breakage of the first layer or the like. Even if a silicon oxide film is formed on the metal wiring layer, the metal wiring layer is not oxidized and the wiring layer of better quality can be realized.
If the first and second layers, or preferably also the third layer are etched in succession into the same pattern, the number of process steps can be reduced. The peripheral wall of the etched metal wiring can be formed to have a normal taper shape.
According to another aspect of the invention, in a liquid crystal display device having a pair of substrates with a liquid crystal layer being interposed therebetween, a plurality of gate electrode wirings, a plurality of drain electrode wirings crossing the plurality of gate electrode wirings, a plurality of thin film transistors formed at cross points between the plurality of gate and drain electrode wirings, and a plurality of source electrodes formed in correspondence with the plurality of thin film transistors, respectively being formed on one of the pair of substrates, at least ones of the plurality of gate electrode wirings, drain electrode wirings, source electrodes, common electrodes if provided, and common electrode wirings if provided are each made of a lamination film including a first layer made of Nb or alloy containing Nb as a main component thereof and a second layer made of nitride of Nb or alloy containing Nb as a main component. With this lamination film, the resistance to thermal oxidation can also be improved. If the lamination film is used as the gate electrode wiring, the improvement is particularly good. If the resistance of the metal wiring poses not practical problem, the metal wiring may be only the second layer made of nitride of Nb or alloy containing Nb as a main component, by omitting the first layer made of Nb or alloy containing Nb as its main component. With this single layer structure, the resistance to thermal oxidation can also be improved.
It is preferable to form a third layer made of nitride of Nb or alloy containing Nb as a main component, under the first layer.
If an insulating film of silicon oxide is formed on the lamination metal wiring made of the first and second layers is formed, the wiring layer of better quality can be realized.
If the electrode structure of the invention is applied to the gate electrode wiring, it is preferable to uses the silicon oxide film as at least a portion of the gate insulating film of a thin film transistor.